Moscow — Following a night of violence and mass arrests in Minsk, Belarus, the state-dominated media on Monday declared that Alexander Lukashenko, the Belarussian leader who's often described as "Europe's last dictator," has been reelected to an unprecedented fourth term with a 79.7 percent majority of the votes. None of his eight opponents won more than 3 percent.

After state-conducted exit polls indicated the scope of Mr. Lukashenko's triumph Sunday night, an estimated 20,000 opposition supporters attempted to rally on Minsk's central Independence Square to protest what they allege to be systematic fraud in the electoral process – as they did under almost identical circumstances in previous presidential polls four years ago.

But this time, authorities reacted with a harshness unseen in the past. An attempt by some opposition supporters to storm the Central Electoral Commission headquarters failed to get past massed ranks of police. Special riot squads then charged into the crowd, using batons and stun grenades, arresting 600 and injuring dozens.

During the night, Belarus's KGB security forces swept through Minsk, arresting six opposition candidates along with scores of their supporters in an operation that continued in full swing Monday. Two of the candidates, Nikolai Statkevich and Vladimir Neklyaev, claimed they were beaten by special police before being taken to prison. The arrested leaders could face jail terms of up to 15 years.

"It's possible that some opposition forces deliberately provoked the authorities in order invite a tough response," says Svetlana Kalinkina, editor of the independent Narodnaya Volya weekly newspaper. "The leaders are all under arrest, so we can't get any explanations from them. But what I don't get is why the police, even if it's their job to impose order, had to use such brutal methods, leaving so many people badly injured."

Yaroslav Romanchuk, candidate of the United Civil Party, was out when the KGB came to his home in the middle of the night and thus avoided arrest. Reached by phone Monday, Mr. Romanchuk said the attempt by some protesters to assault a government building was unfortunate, but it doesn't justify the massive crackdown that's now under way.

"This is a serious cleanup operation, and almost all leaders of opposition groups have already been arrested," he says. "We fear the authorities intend to liquidate all political parties. I really hope the situation doesn't turn tragic."

Belarussian authorities accuse the opposition of attempting to destabilize the country. But the US Embassy in Minsk issued a statement Monday saying, "we are especially concerned over excessive use of force by the authorities, including the beating and detention of several presidential candidates and violence against journalists and civil society activists."

Lukashenko, a former collective farm director, has run Belarus since being fairly elected in 1994. His seemingly unshakable authority is based on his tough control of all the country's guiding institutions and his ability to distribute the fruits of the country's largely nationalized economy – in the form of wages, pensions and guaranteed jobs – to all sectors of the population. Until recently, the Kremlin helped to keep Lukashenko in power with annual subsidies estimated to be worth up to $8 billion.

"I would not doubt that he could win 60 percent of the votes, even now, but 80 percent is not credible," says Fyodor Lukyanov, editor of Russia in Global Affairs, a leading Moscow foreign-policy journal. "And the arrest of all the opposition leaders is very difficult to explain. Lukashenko may have won, but his next term is going to be extremely difficult. People are starting to get very tired of him."

But on Sunday, Russian election observers were quick to endorse Lukashenko's victory as legitimate. "We believe that these elections were transparent and met the requirements of the election legislation and common democratic norms," Sergei Lebedev, leader of the Commonwealth of Independent States' monitoring team told reporters in Minsk. "Our mission has not uncovered facts that would shed doubt on the legitimacy of these elections."

In a preliminary assessment offered before the violence and arrests of Sunday night, the head of the Organization for Security and Cooperation in Europe's observer mission, Gert Arens, appeared to agree. "We have come to a common ground that this election can be assessed better than the previous one," Mr. Arens told reporters.

Critics say the changing attitude of Europeans may be due to Lukashenko's recent efforts to wean himself from Russian influence and woo the West. In October, the European Union dropped longstanding sanctions against 35 top Belarussian officials and even promised Lukashenko a $3.5 billion aid package if Sunday's election went well.

Opposition activists say they did notice an improvement of conditions during the campaign, including easier access to voters and an easing of the police harassment they had experienced in the past.

"Everything was going better than usual this year," says Lev Margolin, campaign organizer for the United Civil Party. "But at some point, Lukashenko decided that was enough tolerance and ended the performance. The leader of our own party, Anatoly Lebedko, is in a KGB solitary confinement cell just now, and our candidate, Romanchuk, is on the run. Maybe now that he's won, Lukashenko doesn't think he needs to impress the West anymore."